Dark Reactive Oxygen Species (ROS) Generation in ReVO4:Eu3+ (Re=Gd, Y) Nanoparticles in Aqueous Solutions

Nanomaterials, which promote the generation of reactive oxygen species (ROS) and precipitate the onset of oxidative stress responsible for the development of a variety of adverse conditions, are of great prospect for various nanomedicine applications.In this paper, for the first time, we report pro-oxidant activity of GdYVO4:Eu3+ and GdVO4:Eu3+ nanoparticles (NPs) in water solutions without any external stimuli (in the darkness). This dark pro-oxidant activity is shown to be associated with superoxide (O2∙-) and hydroxyl radical (●OH) generation and depended on the size of NPs and, consequently, concentration of surface defects, such as oxygen vacancies VO. For small 2 nm GdYVO4:Eu3+ NPs, strong O2∙- and ●OH radicals production has been revealed, whereas for larger GdVO4:Eu3+ NPs, low level of O2∙- and negligible one of ●OH radicals production during sample storage in the darkness have been detected. Possible mechanisms of dark ROS generation in ReVO4:Eu3+ NPs are considered.